TWI409452B - Optical ultrasonic observation device and method for delay synchronization control thereof - Google Patents

Abstract

The invention discloses the Schlieren type ultrasonic wave observer system. The invention states optics interference by the ultrasonic wave sound field after perturbation the medium, and combines to make the interference penetration optical projection the image, the goal lies in the observation ordinary naked eye blind ultrasonic wave sound field distribution. Characteristic of the invention using the spectroscope and the reflector combination, as well as microcontroller precise time delay control, might formerly be limited under the 4F optical field length limit to enhance largely the field of vision the several fold.

Description

Optical ultrasonic observation device and method for delay synchronization control thereof

The present invention relates to an observation device for observing schlieren, and more particularly to an optical ultrasonic observation device capable of observing schlieren.

The Schlieren phenomenon was first discovered by the British inventor Robert Hooke in 1665, and then by the German scientist August Jose Ignaz Toepler to create the world's first schlieren photography ( Schlieren Photography) device.

The technical principle of the so-called photographic device is because when the light penetrates the transparent medium with uneven density, the refractive index of the transparent medium changes with the density, and the direction of the light beam that can penetrate there is also folded. Qu, the schlieren photography device utilizes the disturbance of the light wave by the fluid, and presents the geometry and concentration of the density unevenness in an optical observation manner, and converts the flow field that cannot be seen by the naked eye into a visible image, thus It can take the form of airflow (or water flow) that is not visible to the naked eye, and can be transmitted through different media such as liquids, gases or solids to observe fluctuation characteristics or changes in hot air conduction.

Generally, in the optical architecture system of the conventional schlieren imaging device, an adjustable blade edge, a lampshade source and a group of lens groups are usually included, so that the image can be directly observed, such as the conventional schlieren shown in FIG. Optical architecture system for photographic devices. However, due to the variety of optical components and the limitation of the depth of focus of the lens, the system is bulky and unfavorable. The optical components are very expensive equipment, and the larger the area of the lens, the more expensive it is, and the order is not easy, so the price It is not generally affordable, and it is often impossible to customize a larger lens. Therefore, the image field of view is limited, and the entire ultrasonic image cannot be collected at one time.

As shown in Fig. 2, it is a conventional spatial filter system (such as optical signal processing or Fourier optical conversion system), the so-called 4x focal length (4f) system, when its laser is expanded by a beam expander. After the beam, it becomes parallel light, and after passing through the object plane, the coordinates are (x ₁ , y ₁ ), and the light wave passing through the object plane is the object function f(x ₁ , y ₁ ), and the light wave is reached by the lens 1. The back focal plane (spectral plane or edge) can obtain the spectrum of the object function, the coordinates are (u, v); then through the lens 2, the image plane of the lens 2 can be equal in size and completely similar, but the coordinates are completely The inverted image is set to (x ₂ , y ₂ ); and the coordinates are completely inverted to obtain the exact same image as the original. The system has only one light field (about 5 cm in diameter), so when observing the entire ultrasonic sound field, it requires two panning shots, which increases the difficulty of shooting.

In the prior art, for example, the patent document No. 4,681,437 of the US Patent No. 4,681,437 has a set of optical schlieren systems, and proposes a technique of erecting the schlieren method, but does not aim at the large and small fields of the field of view and its application. Have any advanced advice.

In U.S. Patent No. 3,847,484, although a laser has been used as a light source for an optical schlieren system, a laser source is more suitable for use in a striated system than other sources, and does not require water cooling. Cooling down, but still does not mention the size of the light field formed and its practical application.

In the patent document No. 5,515,158, a single-lens reflex-focusing schlieren system is constructed, which is a smear system that uses lens reflection to concentrate the light source, and when the schlieren system is a light source Through the flow field to the reflection grating, a piece of reflected light can be generated, and after the reflection returns, the flow field is penetrated to the first lens and then imaged behind it, but the control end design and expansion are not mentioned yet. The application of the light field.

In the patent document No. 3582185, the invention relates to a schlieren optical system, comprising a control system for controlling illumination of a light source and a barrier system, as if the mirror arranged in the chess is located on the light path, the lens has been erected. In the light path, although the shielding system can be provided on the image of the light path, and the passage of light can be prevented or allowed, the optical imaging structure of the schlieren system and the expansion method of the system thereof are not mentioned.

In the process of imaging the optical system, if a plane pattern is placed on the front focal plane of an ideal lens (Fourier transform lens), an accurate Fourier transform can be obtained on the back focal plane of the lens to obtain its spectrum. function. Conversely, if the spectrum of a planar pattern is placed on the front focal plane of an ideal lens, the planar image can be obtained from the back focal plane of the lens (but if the coordinates of the graphic are reversed). If it is known from the communication theory of electronics, if the spectrum of the signal is filtered and then the signal is restored, the noise of the signal can be removed; therefore, the communication theory can be compared on the back focal plane of the lens. When a light bar of various shapes and sizes is placed to change the spectrum of the pattern, and then the second lens is imaged, the processed image is processed by optical signal, and on the back focal plane of the lens. The light bar placed is the so-called spatial filter.

Therefore, in summary, the lack of prior art includes the following:

1. The traditional optical schlieren measurement system is bulky and not portable, which is not conducive to the development of commercial products.

2. The field of view is limited, so the entire flow field displayed cannot be observed at one time.

3. When expanding the light field, it is necessary to purchase a larger lens, which leads to an increase in production cost and is not easy to customize, which is not conducive to general commercial development.

4. Timing synchronization is not possible and there is no adjustable micro-control single-chip core technology.

Therefore, in order to improve the measurement efficiency of the optical striated measurement system, and in order to enable the observation of the whole flow field, thereby generating more efficient ultrasonic measurement, it is extremely necessary to develop a new optical schlieren measurement technology. Improve the efficiency of optical schlieren measurement systems and reduce development time and associated manufacturing costs.

It is an object of the present invention to provide an optical ultrasonic observation apparatus for observing schlieren and improving the performance of ultrasonic measurement.

The optical sound field measuring device of the present invention comprises a combination of a continuous laser light source, an optical lens, a water tank, a spatial filter and a charge coupled device detector, and a computer.

The invention adopts a light field focusing lens to directly image on the charge coupled device detector in the design of the optical path, so that it is not necessary to perform secondary imaging through the lens, and the optical signal can be enhanced and the texture of the sound field can be compared. More obvious.

In the overall optical architecture, the angle and matching of the beam splitter and the mirror are used to multiply the previously limited field of view light field by a factor of several times, and the field of view of the spectroscope can be increased according to the actual demand. Light field.

The beam expanding light field used in the present invention can reduce the overall cost by using a beam splitter and a mirror, and is more conducive to the development of commercialization.

The invention adopts a 45-degree angle quartz glass inside the water tank, which can change the path of the ultrasonic wave and become the direction of the ultrasonic axis, so that the wavelength of the ultrasonic wave and the accurate position of the focus can be observed.

The optical unit and the ultrasonic control unit of the present invention are connected to the control core by a single-chip micro-controller, and the single-chip micro-controller is used to adjust the delay time to achieve accurate synchronization of the speed of light and the speed of sound.

The invention is used for observing the ultrasonic wave wave propagation, and can observe the focusing motion of the ultrasonic sound field texture, and perform auxiliary transmission of image information.

The invention is characterized in that the use of a combination of a beam splitter and a mirror, as well as precise time delay control of a single wafer, can greatly increase the field of view by several times under the conventional limited optical field length limit of 4 times the focal length.

In the observation of the direction of the ultrasonic axis of the present invention, the ridge image of the concentric circle can be observed, and the wavelength and the focus position are calculated.

The invention is suitable for collecting the ultrasonic focusing information of the whole process, so it is advantageous to observe the distribution of the sound field energy of the energy wave after penetrating the foreign matter (such as skull, rib, biological tissue, etc.), if the ultrasonic wave can be observed in advance through the heterogeneous object. The location can improve the accuracy of the thermal treatment location.

Therefore, the advantages and spirit of the present invention can be further understood from the following detailed description of the invention and the accompanying drawings.

The invention relates to an optical ultrasonic observation device and a using method thereof, thereby improving the temperature and elasticity effect of the ultrasonic wave, thereby improving the measurement performance.

As shown in Fig. 3, the principle of the 3x focal length (3F) system of the present invention is that the system can display the effect of schlieren with a focal length of 3 times, and even has a stronger image contrast. As shown in FIG. 3, the present invention diffuses a laser light source into a parallel light via a spatial filter. After the parallel light passes through the plane of the object, the focal length is 1 time, and the parallel light path is passed through a plano-convex lens. The collected image is focused and converged. At this time, it is 2 times focal length. After the final focus, the image is displayed on the barrier. At this time, it is 3 times focal length.

As shown in FIG. 4, an optical device portion of an optical ultrasonic observation apparatus of the present invention includes a continuous laser source (CW) 401, an attenuation lens 402, an objective lens 403, and a pinhole 404 (objective lens). 403 and pinhole 404 may be combined as a spatial filter), beam expander 405, water tank 406, optical lens 407, charge-coupled device (CCD) detector 408, and computer 409 are combined.

Still, as shown in FIG. 4, the optical device portion of an optical ultrasonic observation apparatus of the present invention, wherein the relevant position is from the continuous laser light source 401, the attenuation lens 402 is arranged, the objective lens 403 is arranged, and the pinholes 404 are continuously arranged. The beam expander 405 is arranged, the water tank 406 is arranged, the optical lens 407 is continuously arranged, and the charge-coupled device (CCD) detector 408 and the computer 409 are finally arranged.

In the fourth picture, the captured image is a cluster wave, so when capturing the image, it must be synchronized with the ultrasonic wave, the laser, and the camera, because the ultrasonic sound speed in the water is 1480 m / s, and the speed of light It is 299,792,458 m / s, so the laser and camera shooting time must be delayed to capture the image. The system control uses the computer software LabVIEW program to establish the remote control system (GUI), and all components use the interface bus (GPIB) and RS-232 (EIA-RS-232) serial data communication interface standard as the connection. The mechanism includes the frequency setting of the signal required by the ultrasonic probe, the amplification of the RF amplifier, and the monitoring of the output power by the power measuring device; therefore, the output result can monitor and capture the original image signal in real time.

Still, as shown in FIG. 4, an optical device portion of an optical ultrasonic observation apparatus of the present invention, wherein a continuous wave laser light source 401 emits a light beam, passes through the attenuation lens 402, and causes the light beam with a plano-convex lens 403. It becomes a parallel light, and enters the beam expander 405 by the pinhole 404 (that is, the spatial filter combined by the objective lens 403 and the pinhole 404), and the parallel light is uniformly and expanded by the beam expander 405 to become about A parallel light field of 5 cm (cm), and the expanded parallel light field passes through the beam splitter 405A of the beam expander 405, and then diverges into two optical paths, such as a parallel beam and a parallel beam. Then, the parallel beam is reflected by the mirror 405B of the spatial filter 405, so that the parallel beam is parallel with the reflected parallel beam of the previous one, and the two sources are tangent but do not overlap to form an inverted 8-shaped light field. In the water tank 406, the inverted 8-shaped light field penetrates the water tank 406, and the collected image is focused and converged via the plano-convex lens 407, and is imaged on the charge coupled device detector 408 after the focus convergence is completed. And passed to the computer 409 display. In addition to multiplying the optical field, the present invention can also make the optical path turn, so as to reduce the design of the overall body. The design is to image a parallel light passing through the object to be tested, focus it through a plano-convex lens, and directly image it onto the light sensor of the charge-coupled element detector 408, and the position is the virtual image after the focus. Displayed on the screen of computer 409 via charge coupled device detector 408.

Figure 5 shows the working principle of the beam expander 405, which can expand the field of view field to multiply, including the front view, the upper view, the right view, and the 45 degree view. The splitter 405A and the mirror 405B are used. The collocation is adjusted with its angle adjustment, and the limited field of view of the light field is multiplied. Since the beam splitter 405A can divide the light into two optical paths with nearly the same energy, the light field of the single track can be evenly divided into two optical paths with an angle of 45 degrees (the angle can be controlled by the visual demand). Since the incident angle is equal to the exit angle, when the incident angle is 45 degrees, the angle is 45 degrees, so that the optical path can be turned 90 degrees, and the optical path is converted into a mirror 405B with a 45 degree angle. The same light field parallel to the previous optical path, and the beam splitter 405A and the orthographic projection of the mirror 405B are tangent, the two separate light fields can be approximated as close as possible to form an inverted 8-shaped multiplied light field. And a plurality of beamsplitters can be added to perform an infinite expansion of the light field.

As shown in Fig. 6A (refer to the beam expander 405 in Fig. 4), the double beam expander can expand the beam splitter to two, that is, one mirror plus one beam splitter. The beam is expanded to 2 times. As with the 3x beam expander shown in Fig. 6B, the beam splitter is expanded to 3, that is, with 1 mirror plus 2 beamsplitters, the beam can be expanded to 3 times. In addition, as shown in Fig. 6C, the multiple (N-multiple) beam expander can expand the beam to N by expanding the beam splitter group to N slices, that is, by adding one mirror and N-1 beam splitter. Times, and N times is a natural multiple. The beam expander can be expanded in the optical system of the present invention, and has the function of expanding the light field, so that the shooting time of the second translation can be reduced, and the cost is reduced, and the whole process of "sound wave" can be observed at one time. Sound field shadow image.

As shown in Fig. 7, the wavelength and focus are observed in the direction of the ultrasonic axis. The quartz glass can be placed in the ultrasonic sound field path, that is, a 45 degree angle is installed in the water tank 406. The principle of use is to use the physical definition that the incident angle is equal to the exit angle, and the path of the ultrasonic wave changes the 90 degree turn. Further, it is parallel to the ultrasonic axis direction of the charge coupled device detector 408. At this time, the image captured by the charge coupled device detector 408 is a concentric circle (light and dark circular distribution) of the schlieren image, and the black dot in the middle As the focus position, the bright lines are peaks and the dark lines are troughs. The distance between the peaks and the peaks is calculated to be 3.75 mm (mm). The size of the picture and the actual size of the aperture are measured and calculated by the proportional relationship. The wavelength is equal to 3.75 mm (ie, coincides with the ultrasonic wavelength of 400 kHz), thus indicating that this observation method is suitable for measuring the wavelength of ultrasonic sound waves.

The eighth figure is an ultrasonic concentric circular shadow image in the direction of the ultrasonic axis under different timing transients.

Figure 9 is a complete schematic view of an optical ultrasonic observation apparatus of the present invention, and also refers to the description of the optical device portion of the present invention in Fig. 4. As shown in FIG. 9, the optical device portion shown in FIG. 4 is included, and the single-chip micro-controller device 911 is connected to the computer 409 shown in FIG. 4, and the signal generator 912 is continuously connected, and the amplifier is connected. 913. Finally, the focused ultrasonic 914 is connected to generate a supersonic source; wherein the single-wafer micro-controller device 911 is coupled to the continuous laser source 401 to directly activate the continuous laser source 401. The present invention activates the single-wafer microcontroller device 911 by the computer 409, which activates the signal generator 912 and transmits a signal to the amplifier 913 for amplification to control the focused ultrasound 914. The single chip microcontroller device 911 can transmit signals to the computer 409 to control the capture time of the charge coupled device detector 408.

FIG. 10 is a method for delay synchronization control of an optical ultrasonic observation apparatus according to the present invention. The delay signal is manufactured by the internal loop of the single-chip micro-controller 911, thereby controlling the timing, and then according to different needs of the multiple instruments. And the plurality of delay signals are given, and the plurality of delay signals are transmitted to the computer 409 for a parameterized control, so that the computer 409 only needs to select the laser 401 on time (the effect of brightness and darkness may occur), and the signal generator 912 is turned on. Time (wavefront position) and photographing time of the charge coupled device detector 408 (having a bright and dark effect). The computer 409 is controlled by the graphical interface of the LabVIEW computer software, the LabVIEW software is used to control the parameters of the single-chip microcontroller, the function of the signal generator 912 is selected, and the gain value (Gain) of the power amplifier 913 is selected. The invention can capture the progress of the "sound wave sound field". The FG in Fig. 10 is the signal generator, and the N in the figure is the first signal that is played. Therefore, in order to capture a complete wave, to grab a certain signal as a starting point, at this time, the ripple is still not visible from the charge coupled device detector 408, and each time the FG and the charge coupled device detector 408 are opened, It will increase for a small time (4.125 microseconds). Since the FG off time is fixed, the FG and the charge coupled device detector 408 can be spaced apart to determine the wavefront position, or can be set as a loop, so that the wave can be continuously captured. The march.

According to the test result of the present invention, the skull cover of different thickness around the brain chamber of the pig is selected as the experimental test material, and the area of about 35 mm×35 mm is 2 mm, 3.5 mm, 6 mm and completely. There are four images of the skull. A peak-to-peak voltage of 500 millivolts (mV) was supplied via a signal generator, and the power was amplified by an amplifier, and a clustered wave was emitted from a 400 kHz probe of a focused ultrasonic wave. The experimental results are as follows.

The schlieren image shown in Figure 11 (without any pig skulls) is a 400 kHz cluster wave image, that is, the image transmitted by the visible wave at increasing timing, the ultrasonic wave is made up of arrows Directional delivery. The signal generator parameters are set to a peak-to-peak value of 500 millivolts (mV), the number of cycles is 10 loops, and the Pulse Repetition Frequency (PRF) is 500 Hz. The delay circuit sets the control charge coupled device detector 408 to capture the image every 1.8 microseconds (μS), while the laser 401 turns on for 5 microseconds every 1.8 microseconds.

Fig. 12 is an image view comparing the pig skull of 2 mm thickness with that of Fig. 11.

Fig. 13 is an image view comparing the pig skull of 3.5 mm thickness with that of Fig. 11.

Figure 14 is an image comparison of the pig skull of 6 mm thickness after comparison with Fig. 11.

In the foregoing FIGS. 12 to 14, when the probe is turned on, the charge coupled device detector 408 and the laser 401 can be triggered to capture images by an additive manner at intervals of 1.8 microseconds. Therefore, it can be clearly seen on the graph that as the thickness is thickened, the penetrating energy sound field will be weakened, and the focal position and pressure distribution of the ultrasonic sound field can also be seen, and because the skull is an irregular surface. Therefore, after the ultrasonic wave has penetrated, the focus position will change, so the direction of the focus position after passing through the skull can also be observed. The field of view field is about 10 cm (one circle is 5 cm in diameter), so The full-range focused ultrasonic forward motion can be observed. The experimental results show that the "sound field" of the 400 kHz focused ultrasound can prove that the optical striated system can effectively observe the focus or divergence of the ultrasonic wave after penetrating the foreign matter.

Further, Fig. 15 is a view showing a sound field distribution measurement of an industrial ultrasonic wave transmitted through the optical system of the present invention. The frequency of the sound field is 28 kHz, and the wave field distribution shown in the figure can be clearly observed. It can also be confirmed that the frequency level of the invention near 20 kHz can also be successfully observed, so the system of the present invention can be applied to biological In addition to the observation of medical ultrasound, it can also be applied to the sound field observation of industrial-grade ultrasonic systems.

Therefore, in view of the above, in terms of the optical path component system, the 3x focal length system of the present invention is significantly smaller in size and compared with the conventional 4x focal length (4F) system and the 3x focal length (3F) system of the present invention. The beam expanding function eliminates the need for a secondary panning image, and the volume and image quality, as well as the shooting time, are greatly improved. The invention is characterized by the simplification, combining the ultrasonic sound field with the focused ultrasonic wave, multiplying and expanding the limited observation field light field, and performing the delay synchronization control of the light and the sound by using the single-chip micro controller. Therefore, a transient image of the ultrasonic sound field can be taken, and the entire ultrasonic image can be obtained only once.

The above is only the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention; all other equivalent changes or modifications which are not departing from the spirit of the present invention should be included in the following. Within the scope of the patent application.

401. . . Continuous laser source

402. . . Attenuating lens

403. . . Plano-convex lens

404. . . Pinhole

405. . . Beam expander

405A. . . Beam splitter

405B. . . Reflector

406. . . Water tank

407. . . Plano-convex lens

408. . . Charge coupled device detector

409. . . computer

911. . . Single chip micro controller device

912. . . Signal generator

913. . . Amplifier

914. . . Focused ultrasound

Figure 1 shows the optical architecture system of a conventional schlieren camera.

Figure 2 shows a traditional spatial filter system.

Figure 3 shows the principle of the 3x focal length system of the present invention.

Fig. 4 is a view showing an optical device portion of the optical ultrasonic observation apparatus of the present invention.

Figure 5 shows the working principle of the beam expander.

Figure 6A shows a schematic diagram of a 2x beam expander.

Figure 6B shows a schematic diagram of a 3x beam expander.

Figure 6C shows a schematic diagram of a multiple multiple beam expander.

Figure 7 shows an illustration of the wavelength and focus in the direction of the ultrasonic axis.

The eighth figure is an ultrasonic concentric circular shadow image in the direction of the ultrasonic axis under different timing transients.

Figure 9 is a complete schematic view of the optical ultrasonic observation apparatus of the present invention.

Figure 10 is a diagram of the apparatus for delay synchronization control of the present invention.

Figure 11 shows a 400 kHz cluster wave image.

Fig. 12 is an image view comparing the pig skull of 2 mm thickness with that of Fig. 11.

Fig. 13 is an image view comparing the pig skull of 3.5 mm thickness with that of Fig. 11.

Figure 14 is an image comparison of the pig skull of 6 mm thickness after comparison with Fig. 11.

Fig. 15 is a view showing the sound field distribution measurement of the industrial ultrasonic wave transmitted through the optical system of the present invention.

401. . . Continuous laser source

402. . . Attenuating lens

403. . . Plano-convex lens

404. . . Pinhole

405. . . Beam expander

405A. . . Beam splitter

405B. . . Reflector

406. . . Water tank

407. . . Plano-convex lens

408. . . Charge coupled device detector

409. . . computer

911. . . Single chip micro controller device

912. . . Signal generator

913. . . Amplifier

914. . . Focused ultrasound

Claims (3)

An optical ultrasonic observation apparatus having a double objective field of view, comprising at least: a continuous laser light source; a computer; a single chip micro controller device; a signal generator; an amplifier; a focused ultrasonic wave, wherein The computer is coupled to the single chip microcontroller device, coupled to the signal generator, coupled to the amplifier, and coupled to the focused ultrasonic wave to generate an ultrasonic source, the single wafer microcontroller device being coupled to the continuous laser source Directly starting a continuous laser light source, the computer starts the single-wafer micro-controller device, the single-chip micro-controller device activates the signal generator, transmits a signal to the amplifier for amplification to control the focused ultrasonic wave; Attenuating lens; an objective lens; a pinhole; a mirror and a beam splitter formed by a double objective field expander; a water tank containing a quartz glass having a 45 degree angle; an optical lens; And a charge coupled device detector; After the continuous laser light source excites a light beam, the single-chip micro-controller device transmits the signal to the computer to control a shooting time of the charge-coupled element detector, and the flat beam lens makes the light beam a parallel light. Entering the beam expander from a pinhole, and using the beam expander to uniformly and expand the parallel light to become a parallel light field of about 5 cm, the parallel light field is divided by a beam splitter of the beam expander a penetrating parallel beam and a reflecting parallel beam, the penetrating parallel beam being reflected by a mirror, the penetrating parallel beam being parallel to the reflected parallel beam, the penetrating parallel beam being tangent to the reflected parallel beam but not Overlap, a light field is formed in the water tank that penetrates the water tank, is imaged on the charge coupled device detector via the optical lens, and passed to the computer. An optical ultrasonic observation apparatus having a three-dimensional objective field of view, comprising at least: a continuous laser light source; a computer; a single-chip micro-controller device; a signal generator; an amplifier; a focused ultrasonic wave, wherein The computer is coupled to the single chip microcontroller device, coupled to the signal generator, coupled to the amplifier, and coupled to the focused ultrasonic wave to generate an ultrasonic source, the single wafer microcontroller device being coupled to the continuous laser source Directly starting a continuous laser source, the computer activates the single-wafer microcontroller device, the single-chip microcontroller device activates the signal generator, transmits a signal to the amplifier for amplification to control the focus Ultrasonic wave; an attenuating lens; an objective lens; a pinhole; a mirror and a two-beam spectroscope forming a triple objective field expander; a water tank containing a quartz glass having a 45 degree angle An optical lens; and a charge coupled device detector; wherein after the continuous laser source excites a beam, the single wafer microcontroller device transmits the signal to the computer to control a shot of the charge coupled device detector At a time, the beam is made into a parallel light by a plano-convex lens, and the beam expander is entered into the beam expander, and the beam is uniformly and expanded by the beam expander to become a parallel light field of about 5 cm. The light field is split into a parallel beam and a reflected parallel beam through a beam splitter of the beam expander, and the penetrating parallel beam is reflected by a mirror such that the penetrating parallel beam is parallel to the reflected parallel beam. The penetrating parallel beam is tangent to the reflected parallel beam but does not overlap to form a light field in the water tank, the light field penetrating the water tank, and the charge coupling element is imaged through the optical lens On the detector, and transmitted to the computer. The device of claim 2, wherein the number of beamsplitters in the beam expander is N-1, that is, the N-1 beam splitter forms an N-fold beam expander, and N is greater than 4.